Lincoln Street Substation Transformer Explosion Burbank, CA - 04/10/2020 8

[Mbrooke]

Transformer explosion and fire:

https://www.youtube.com/watch?v=IIMlHjfhb6U

Looks like there was sustained arcing on the secondary before the explosion:

https://www.youtube.com/watch?v=i82WIATHXNY

I'm guessing a short circuit occurred on the 12kv (or 16kv) side with relaying failing to catch/clear it. The transformer remained severally overloaded overheating to the point the oil inside it ignited.

I don't take credit for these picture but to give you an idea that power transformers typically contain anywhere between 7,000 to very well over 25,000 gallons of oil.

https://imgur.com/a/KzJVNKp

https://imgur.com/1wdbAnf

Can I make the claim that my practice of 200E fuses on the primary would have prevented all this?

 

[prc]

argotier, Hope you have referred to edition 2.0 of 76-7 that was published in 2018. They have revised text and formulae completely and very clearly said ( you have also cautioned)that these factors are not applicable to loading above the rated load.

I had occasion to see ( means only photos as I have never seen a transformer fire, though had to investigate many fires) secondary side arcing ( large air filled cable boxes in 125 MVA 33 kV units) due to moisture condensation or failure of support insulators. The effect of arcing in all those cases were minimal.

Before concluding let me narrate an actual case. In a remote village a 315 KVA 3 phase 11/0.433 kV transformer was working at a height-not exactly pole mounted, but on a pole platform. One day it exploded and caught fire and splashed burning oil injuring people in the street below. Found the following: Fuse on primary side not effective; breather pipe closed by a plug as breather was not available. Feeder was tripped by the relay at remote substation indicating a current of 1000A. HV side tank panel completely blasted away, exposing the internal core-coil assembly in full. One school of thought was high pressure developed inside the tank (as breather pipe closed)caused blast. I ruled out this as such pressure increase will be gradual and may cause weld crack and oil leak. Since oil leak was not there before the blast, it cannot be correct. Secondary full bolted short circuit current can create only <400 A on 11kV side. Since it was 1000 A, it must be a low impedance fault. Either secondary side internal fault soon developed in to a primary line to tank fault or primary line end fault to ground, 11Kv line fault MVA collapsing inside tank, high energy release blasting away the HV side panel. Solution as per American literature seems, current limiting fuse + expulsion fuse in series on primary side.

 

[Mbrooke]

FWIW, more food for thought. Nothing succinctly indicates this a transformer, but arcing is seen for a long period of time (guy manages to look outside and then drive to it) until something explodes in a ball of fire:

https://www.youtube.com/watch?v=DPlFflNHU2g

Same event- 1 minute 53 seconds before the ball of fire:

https://www.youtube.com/watch?v=lfLIuaztIuw

And of course the Florida vid from a few years back, its seems like bushing flash-over finally clears the source?

https://www.youtube.com/watch?v=fzbQjd_Oo4Q

Can we just assume that arcing has grand impedance? So much so that it even fails to trip circuit breakers and fails to blow fuses?

https://paceforensic.com/pdfs/Circuit_Breakers_The_Myth_of_Safety.pdf

A real world example of low voltage carbonized arcing- notice the sparks and still nothing:

https://www.youtube.com/watch?v=uPlELdH0KeM

This is a fault in an electrical cable we found at a coolstore - this cable had been run illegally with no physical protection and the 16 Amp fuse had been replaced with a 32 Amp fuse when the fault blew the first fuse. Due to the cable size and length the fault current was not enough to blow the larger fuse - this would have eventually kept blowing until it reached flammable material and a major fire would have started.

I think many fail to realize arcing is between a normal load and a dead short circuit.

 

[Mbrooke]

Hate to nit pick:

Heating up will be faster as copper resistivity will go up when temperature increases.

I've always understood it as resistance going up slowing down the rate of heating. More resistance = less current. Of course I'm open to other factors being at play.

Solution as per American literature seems, current limiting fuse + expulsion fuse in series on primary side.

Yup. Typical with pad mounts and "completely self protected" pole pigs. Also seen it done with stand alone "conventional" pole pigs, see pages 3 and 4:

https://www.eaton.com/content/dam/e...fuse-installation-instructions-mn132009en.pdf

https://www.eaton.com/content/dam/e...-current-limiting-fuse-catalog-ca132021en.pdf

 

[waross]

Thank you prc.
I have no issues with your information.
The point that I am trying to make is that this event was greater than acceptable overloads and less than a bolted fault.
The current was less than maximum due to three factors;
1. An arcing fault.
2. The impedance of the circuit from the transformer to the arc.
3. Voltage drop on the primary circuit.

Some factors we don't know;
How long did the fault persist until the tank ruptured?
We see the white arc on the bus bars generating brown smoke for almost a minute.
The footage was taken from a news helicopter and we have no indication of the length of time that the arc burned before the helicopter started recording.
After the tank ruptures we see red flames and black smoke.

What was the initial cause?
There was a suggestion, as yet unconfirmed, that a car may have hit a power pole.
If so then magnetic forces may have torn a connection loose on the bus bars to start the arc.
More likely a bird or rodent started the arc.

prc, Is it reasonable that a current in the range of 250% to 350% could result in failure in several minutes?

Other than that, we can not speculate much more until we get more information.






Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

Somewhat off topic, but (2/3 of the way through this PDF) testing was done on a fire fighter's ability to spray water on energized equipment. Live 345kv was used in part of the test. Surprisingly current is only in the milli amp region:

https://www.nfpa.org/assets/files/AboutTheCodes/18A/18A_F2016_WAB_AAA_SD_Ballot_final (002).pdf

If it helps, from page 37:

https://imgur.com/a/m1SuYm5